Manufacture of strings and the construction thereof



NOV. 25, 1958 J, CRANDALL 2,861,417

MANUFACTURE OF STRINGS AND THE CONSTRUCTION THEREOF Filed June 16, 1954 INVENTOR. Jar/x272 7T frarzdzll "Mid/M Arnrzwy United States Patent "ice MANUFACTURE OF STRINGS AND THE CONSTRUCTION THEREOF Julian T. Crandall, Ashaway, R. 1., assignor to Ashaway Line & Twine Mfg. Co., a corporation of Rhode Island This application is a continuation in part of application Serial No. 241,065, now U. S. Patent No. 2,735,258, filed August 9, 1951, for Manufacture and Construction of Strings.

The present invention relates to the'manufacture of strings for stringing tennis, badminton and squash racquets and for musical instruments, and has particular reference to a novel manufacture and a novel construction therefor.

The principal object of the invention is to provide an improved string for tennis racquets, musical instruments, and the like. 7 7

Another object of the invention is to provide an improved string comprising a filament core and an integrally joined sheath.

A further object of the invention is to provide an improved string having great strength, elasticity, and resistance to fatigue and distortion.

A further object is the provision of a spirally wound sheath construction for a core of linear filaments, the sheath and corebeing bonded together and the sheath winding resisting unwinding and fraying. I

With the above and other objects and advantageous features in view, the invention consists of a novel method and a novel article more fully disclosed in the detailed description following, in conjunction with the accompanying drawings, and more specifically defined in the claim appended thereto.

In the drawings,

Fig. 1 is a perspective view of a tennis racquet strung with the improved string;

Fig. 2 is an enlarged portion of the string, parts being broken away to show the elements thereof; and

Fig. 3 is a perspective enlarged view showing the appearance of the string during the different stages of manufacture.

It has been found desirable to provide an improved string for tennis racquets, and the like, which has great strength, is very resilient, with great resistance to tension strains, flexing, separation of the parts thereof, and which has a smooth water repellent outer surface. To this end, I have devised a composite construction which utilizes a center flexible core of high resiliency, preferably made of linear synthetic plastic filaments, and a tough composite armor sheath, preferably including a textile winding and a synthetic plastic filament winding, the sheath being integrally locked to the core to provide a smooth, hard, abrasion resisting string with an outer smooth coating, and the winding being designed to resist unwinding and separation from the core.

I have found that a suitable plastic for such strings is 2,861,417 Patented Nov. 25, 1958 core 12 which is flexible and of high resiliency and an armor sheath 13, which is tough and wiry, the core and sheath being integrally locked together, preferably with synthetic plastic 14. The resulting string has an integrated linear core and'a wound sheath with a smooth outer coating, is hard and tough, and does not abrade when pulled through the string holes of the racquet.

The improved string ismanufactured by first forming a core of adjacent linear strands as indicated by the reference numeral 15 in Fig. 3. This core is passed through a tank containing a solution of a special coating material, which preferably has a nylon base, it being preferred to apply several thin layers of a coating rather than a single heavier layer. The coated core may be lightly brushed to obtain a smooth finish, as indicated by thereference numeral 16, and then air dried, and textile thread is wound spirally over the coated core in a clockwise direction as indicated by the reference numeral 17. The covered core is again coated by passing through the integrating solution, preferably to obtain several thin layers, and may be again lightly brushed to provide a smooth coated covered core as indicated by the reference numeral 18. The coated textile wound core is now airdried; a second spiral winding 19 of a plastic thread, preferably nylon monofilament, is wound over the smoothed coating 18 in an anti-clockwise direction, and is coated in the integrating solution, and lightly brushed to smooth the surface as indicated at 20. The assembly is now subjected to predetermined heat conditions, to form a completely integrated string, as the three coatings soften under heat and pressure to lock the parts together, the string being stretched, indicated by the reference numeral 21, and quickly cooled, either by air or by passing through a water bath; the'r'esulting product is a strong, completely integrated string having a highly resilient for musical instruments, the number and extent of the coatings are regulated to provide a desired tone.

Although I have found that synthetic resin solutions may be used for integrating the string, a satisfactory coating solution includes nylon, dissolved with isopropanol and tetrahydrofurfuryl alcohol in a water base, the proportion of nylon being variable between the limits of 10 to 25% by weight, of isopropanol between the limits of 50 to 70% by weight, and of tetrahydrofurfuryl alcohol between the limits of 5 to 20%, by weight, the proportions being chosen and suflicient water being added to provide a coating solution of suitable consistency.

Two specific formulae that have been found suitable for the desired coatings are as follows, based on a sixtypound batch:

Tetrahydrofurfuryl alcohol 10 The nylon, which is preferably of shredded type, is added to the other ingredients under heat to form the coating solution, and the proportions of the ingredients are varied to provide a. clesiredzstifiness in the final pr oduct. For stringsrequiringmore flexibility, it :is desirable to add a predetermined amount of plasticizer. It has been found that a string whichthas a diameter -of 10.56 inch before integration will breakunder a deadiload of one hundred pounds; after integration and stretching, with a diameterreduced to .050 inch,the-.break load has risen to one hundredtenpounds.

The integration rdrawingsforalstring of the size described is referablywunder a strain load :of fiftypounds, using a drawing ispeed of about :eight hundred iyardsper hour and aternperatureof substantially 360 -F. The resulting string :has athesstiffness suitable ,for use in tennis racquets and the like. Change in drawing speed, pull and temperature will ;pro,du,c e a mariation in the stiffness; therangenf speed ;is from :two hundred to one thousand yards per, 11, and the range of temperature is 'from .250 to-400" F.

A string made as described has high tensile strength, very high resiliency when strung, and great resistance to fatigue, distortion and separation of the sheath from the core, whereby -.the,racquet strings holdtheir shape, give long wear, are water. repellent, anddo not elongate or stretch with continued use. When the string is made of nylon, the linear core-provides high resilience and the sheath provides great resistance to abrasion; molecular orientation is produced by ihe stretching and is fixed by'the quick cooling.

For certain string constructions the textile winding may be replaced by aplastic winding-to provide an all plastic string. The preferred material for the core :is linear multi-filament nylon, which has high elasticity and resilience, the individual filaments being-as-small as ..O02 inch in diameter. The preferred material for the :spir-al'layers is vmonofilament nylon of larger cross section, such as .008 inch in diameter, which produces a hard,-tough wearing surface, the spiral winding having substantially ;no eflect onthe resiliency of the multi-filament core al though integrated'with the core.

Other suitable plastic monofilament material o f the polyamide, vinylite and polyester type may be used for composite strings having different characteristics for dif ferent uses, with textile and silk cores as sheaths, and in combination with plastic materials, suitable binders being utilized to integrate the flexible material core with a cover or sheath of tough material.

Although I 'havetdescribed a specific stringrconstruction having particular characteristics desirable for racquets and musical instruments, it,is obvious that string made ,as disclosed herein may beused for other purposes, such as for example for fish-hook leaders and fish- 8 nes, and thatnhangesiin the sizeandtshapetof the Referenoesfiited in the file=ofgthis patent LUNL'IEED -.=S?EAEES PAT EN "ES 1,772,846 Spolidoro Aug. 12, 1930 1,970,375 -Hamburger Aug. 14, 1934 -2,'091;999 '-Madge et-al.' Sept; 7,1937 2,157,117 Miles .May '9, 1939 2,205,144 Kaplan June 18, "1940 2511;704 simison Feb.23, 1943 2,335,644 Camp --l- TNOV."3Q, {1943 2,401,291 Smith -May 28, 1946 2,-521;055 Foster Sept. 5, 1950 2,649,833 Crandall Aug.25, 1953 Crandall -Feb. 21, 1956 

